I think, it must be known already but still:

BUG 1:

1. Make a FRX. The Dataenvironment consists of two views and both AutoCloseTables and AutoOpenTables are .f.. Put some fields on the Report.

2. Open the report in designer with Modify Report
3. Try PrintPreview
4. Cancel the GetFile-Dialog without opening anything.

The Report-Designer disappears and all further attempts to Modify Report stay without any reaction. On certain Actions (e.g. you try to compile a project with this frx in it) you get "File in Use" - message. It looks like the Report Preview Window is still active but invisible. CLOSE ALL helps.
Nothing of the kind happens with REPORTBEHAVIOR 80.

BUG 2: (or is it not a bug?)

With REPORTBEHAVIOR 80 (and as long as I can remember myself) if there is a syntax error, the execution of report stops, the wrong expression is shown and you can change it or at least you know where the error is. With REPORTBEHAVIOR set to 90 I either get no message at all (the Report just will not be executed), or the message is "Synthax Error" without to tell where and what is wrong. I could not figure out, which comes when, but in the second case all objects in report after you confirm the error message are suddenly selected (dots everywhere)

There are also other issues... Schould one stay at REPORTBEHAVIOR 80 for some time yet?