File not found with external diff tool (BeyondCompare)

With SourceTree version 3.0.8, the external diff tool works only for the first selected file. All additional files display a "file not found" error message. SourceTree shows the differences correctly. We are using BeyondCompare version 4.2.8. Earlier SourceTree versions worked fine.

Example to reproduce:

• select a commit with several changed files
• in the "Log/History" tab select one file (A) and show the differences in BeyondCompare (ctrl D in our case) --> the differences are shown in BeyondCompare as expected
• in SourceTree select another file (B) and show the differences --> BeyondCompare shows "file not found" for both sides; the same effect is for all additional files as long as the BeyondCompare is open.
• close BeyondCompare
• in SourceTree select file B and show differences --> BeyondCompare OK
• in SourceTree select file A and show differences --> BeyondCompare "file not found"