Rodd
On my Windows 7 system I have no problem with the tooltips but my monitor is also 2560x1440. Does your system meet the minimum system requirements for video?
http://www.pixinsight.com/sysreq/index.htmlVideo Hardware
Minimum required display resolution: At least 900 pixels of vertical resolution.
Minimum reasonable display resolution: 1920×1080.
Recommended low-dpi display resolution: 2560×1440.
Recommended high-dpi display resolutions: 3840×2160 (4K) / 5120×2880 (5K) / 7680×4320 (8K).
We strongly recommend a high-end 27-inch or larger LED/LCD panel, or two panels driven by a dual-head video card. For serious image processing, working with large monitors is a real must with PixInsight.
Since version 1.8.4 (released Summer 2015), PixInsight is a fully scalable application supporting high-dpi display resolutions such as Retina displays, 4K, 5K and 8K displays, on all supported operating systems.
You might have a look at the Core UI Resources parameters in the Global Preferences. Maybe they can be tweaked.
Mike