Can you supply more details about your set up? OS? Do you have the latest drivers for the video card? Anything else typically running?
The white "flash" is I believe "as designed". To indicate the file is unavailable during the save.
Windows 7 Pro 64-bit running on Sony VPC-Z1 laptop. 8GB of RAM, very fast SSD. Unfortunately, I cannot compare this to Fireworks CS4, which I used on the same OS but different computer: this laptop replaced my previous machine. FW CS4 worked very well for me. I have no issues thus far with Photoshop, Illustrator, Dreamweaver, or Flash CS5. I was just interested to know if I hit something common with FW. I'll keep poking it under various conditions until I find a reproducible case so that I could file a bug report. Or not
I was not entirely correct. I now also tested this with Fireworks directly opening file, not just "Edit with Fireworks." Initially the "Original/Preview/2-up/4-up" bar is completely absent. But, if I open another document, switch to its tab and switch back to original document, then I can partially reveal bar by hovering mouse over its supposed location.
Also, turning tab into floating document window restores bar and I can then dock that window back, turning into tab, and keep the bar. So, that's a workaround.
And it does not appear to be a video card related as the same exact thing happens and with same random consistency when I switch my laptop into stamina mode (i.e. use built-in Intel chipset graphics).
I'm off to file a bug report with Adobe.