This is a problem I frequently have. I can't custom format a date in the Inspector. I can't make a selection because the drop down menu becomes a long vertical blue stripe and selections are not available. I wonder if this is a FMP problem or a Windows 10 problem. Does any one else have the same problem?

Yes, I am currently having this problem as well.  It's not just FM 17 -- I also experienced this with FM15 which I used previous.  I have to restart my FM client for the problem to resolve itself, and I can't find any pattern as to how/when the issue arises.

I have this issue in FM12 - FM18 on the appearance tab in the inspector for the object state dropdown, but never anywhere else, solution for me was just click the dropdown to show the huge blue list (sometimes is a shrunken blue list) then click somewhere on the inspector outside of the dropdown, you should see the dropdown text is outlined meaning its still the active field, then just use the arrow keys on your keyboard to select the option you wish. Clicking into another inspector field will commit the change.

This has been the only solution i found since FM12, Filemaker really needs to stop letting these silly bugs go on for so long.

I've never experienced this on either macOS or Windows 10 so it may not be a wide-spread kind of thing.  Anyhow; if you feel strongly about the bugs you discover, make sure to report them here: https://community.filemaker.com/en/s/topic/0TO0H000008OQOGWA4

If it requires a change of the feature set, report it here: https://community.filemaker.com/s/ideas and invite people to vote it up.

If you don't then FMI may not hear about your bug or your feature request. And they do pay attention to what comes in on both of those channels.

It's a Windows bug and there have been reports about it for years. It's super annoying.

Sometimes you can get to the selection you want by using the arrow keys. Only other option is to restart the app.

Fair enough.  It's just never bitten me or any of our projects so I wanted to make sure that the channels to report the issue were clear,

https://community.filemaker.com/en/s/feed/0D50H00006ezLwLSAU