Previously, Inkscape didn't check if there's enough free memory for its pixel buffers and could crash without warning due to insufficient memory, e.g. upon zooming in. This problem became much worse after implementing Gaussian blur, because rendering blurred objects at high zooms may require a pixel buffer much bigger than the visible canvas. Now this situation is handled more gracefully: if a display operation requires more memory than available, or more than 100Mb (which corresponds to a 5000x5000 pixel buffer), it is skipped. This may result in blurred objects "disappearing" at high zooms. This is purely a display issue, however, it never corrupts data; just zoom out (or reduce blur radius) and the missing object will show up OK.
The "100Mb" magic number was chosen so that to prevent too large allocations which, even if they succeed, bog the system down to an almost unusable state. I realize it's far from perfect, but at least it's a solution which kinda works for a "typical" system with at least 256Mb memory. Any suggestions on how to better handle this are welcome.