QGIS » QGIS Application

In QGIS 2.18.19 on Ubuntu 17.10, I cannot use the Split Features tool from the Advanced Digitizing Toolbar.

I click the button, and as long as I stay out of the map canvas, everything is OK. When I mouse over the canvas, the cursor changes to the wait spinner, then eventually to teh target icon for pslitt. However, at that point qgis starts using 100% of a CPU and becomes unresponsive. Mousing over toolbar buttons doesn't make them pop out like normal, menus do not work, cannot quit. Ubuntu will eventually ask to wait or force quit, and that or kill -9 is the only way to stop it.

If I start QGIS from a shell, it prints out the following lines when the mouse is moved to the map canvas the first time after selecting the Split Features tool.

src/core/qgssnappingutils.cpp: 409: (prepareIndex) [15504ms] Index init: 4006 ms (gadm28_adm120180521210408156)
src/providers/postgres/qgspostgresprovider.cpp: 2962: (featureCount) [3ms] number of features as text: 4132
src/providers/postgres/qgspostgresprovider.cpp: 2967: (featureCount) [0ms] number of features: 4132
src/providers/postgres/qgspostgresconn.cpp: 1034: (openCursor) [0ms] Starting read-only transaction: 90507
src/providers/postgres/qgspostgresfeatureiterator.cpp: 277: (fetchFeature) [168ms] Finished after 4132 features
src/providers/postgres/qgspostgresconn.cpp: 1052: (closeCursor) [0ms] Committing read-only transaction
src/core/qgssnappingutils.cpp: 409: (prepareIndex) [8ms] Index init: 179 ms (ne_10m_coastline20170815152809945)
src/providers/postgres/qgspostgresprovider.cpp: 2962: (featureCount) [2ms] number of features as text: 234
src/providers/postgres/qgspostgresprovider.cpp: 2967: (featureCount) [0ms] number of features: 234
src/providers/postgres/qgspostgresconn.cpp: 1034: (openCursor) [0ms] Starting read-only transaction: 90507
src/providers/postgres/qgspostgresfeatureiterator.cpp: 277: (fetchFeature) [390ms] Finished after 234 features
src/providers/postgres/qgspostgresconn.cpp: 1052: (closeCursor) [0ms] Committing read-only transaction
src/core/qgssnappingutils.cpp: 409: (prepareIndex) [1ms] Index init: 393 ms (timeline_countries20170817180707420)
src/core/qgssnappingutils.cpp: 412: (prepareIndex) [1ms] Prepare index total: 4580 ms

I've disabled all plugins, nothing changes. This happens in all my projects, including ones I haven't touched for sever months and QGIS LTR updates. I get QGIS from the "http://qgis.org/debian-nightly-ltr artful main" repo.