Internal error "initializing hg cache" after upgrade to mercurial 4.2.1

Created originally on Bitbucket by emrfrazierm (Mitch Frazier)

After upgrading mercurial to 4.2.1 (via TortoiseHg), most (but not all) of my repositories fail to open with the following error message in eclipse:

An internal error occurred during: "Initializing hg cache for: xxx"

Initializing hg cache for: xxx
Refresh status...

An internal error occurred during: "Initializing hg cache for: xxx".
A non-digit found: x    <-- various letters appear here

Appears to be the same issue as described in Issue #525 (closed) (closed as invalid).

Relevant part of eclipse log:

!ENTRY org.eclipse.core.jobs 4 2 2017-07-13 11:52:31.825 !MESSAGE An internal error occurred during: "Initializing hg cache for: bin". !STACK 0 com.aragost.javahg.internals.RuntimeIOException: A non-digit found: f at com.aragost.javahg.Changeset.readListFromStream(Changeset.java:206) at com.aragost.javahg.Changeset.readListFromStream(Changeset.java:176) at com.aragost.javahg.commands.ParentsCommand.execute(ParentsCommand.java:55) at com.aragost.javahg.WorkingCopy.retrieveParents(WorkingCopy.java:115) at com.aragost.javahg.WorkingCopy.ensureParentsRetrieved(WorkingCopy.java:109) at com.aragost.javahg.WorkingCopy.getParent1(WorkingCopy.java:40) at com.vectrace.MercurialEclipse.team.cache.MercurialStatusCache.refreshStatus(MercurialStatusCache.java:776) at com.vectrace.MercurialEclipse.team.cache.RefreshStatusJob.run(RefreshStatusJob.java:88) at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55) Caused by: java.io.IOException: A non-digit found: f at com.aragost.javahg.internals.HgInputStream.decimalIntUpTo(HgInputStream.java:335) at com.aragost.javahg.internals.HgInputStream.revisionUpTo(HgInputStream.java:394) at com.aragost.javahg.Changeset.createFromInputStream(Changeset.java:111) at com.aragost.javahg.Changeset.readListFromStream(Changeset.java:197) ... 8 more

!ENTRY org.eclipse.core.jobs 4 2 2017-07-13 11:52:32.137 !MESSAGE An internal error occurred during: "Refresh status...". !STACK 0 com.aragost.javahg.internals.RuntimeIOException: A non-digit found: f at com.aragost.javahg.Changeset.readListFromStream(Changeset.java:206) at com.aragost.javahg.Changeset.readListFromStream(Changeset.java:176) at com.aragost.javahg.commands.ParentsCommand.execute(ParentsCommand.java:55) at com.aragost.javahg.WorkingCopy.retrieveParents(WorkingCopy.java:115) at com.aragost.javahg.WorkingCopy.ensureParentsRetrieved(WorkingCopy.java:109) at com.aragost.javahg.WorkingCopy.getParent1(WorkingCopy.java:40) at com.vectrace.MercurialEclipse.team.cache.MercurialStatusCache.refreshStatus(MercurialStatusCache.java:892) at com.vectrace.MercurialEclipse.team.cache.MercurialStatusCache$ProjectUpdateJob.updateProject(MercurialStatusCache.java:143) at com.vectrace.MercurialEclipse.team.cache.MercurialStatusCache$ProjectUpdateJob.run(MercurialStatusCache.java:129) at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55) Caused by: java.io.IOException: A non-digit found: f at com.aragost.javahg.internals.HgInputStream.decimalIntUpTo(HgInputStream.java:335) at com.aragost.javahg.internals.HgInputStream.revisionUpTo(HgInputStream.java:394) at com.aragost.javahg.Changeset.createFromInputStream(Changeset.java:111) at com.aragost.javahg.Changeset.readListFromStream(Changeset.java:197) ... 9 more