0. Open the Modular Storage
1. Put one Storage Card into the Modular Storage
2. Shift + other Storage Card
   => First Storage Card are lost

Minecraft 1.12.2 (Forge 1.12.2-14.23.2.2611)

My mods:
appliedenergistics2-rv5-stable-8.jar
BetterBedrockGenerator-1.12-6.1.1.jar
BiblioCraft[v2.4.3][MC1.12.0].jar
buildcraft-core-7.99.14.jar
buildcraft-factory-7.99.14.jar
buildcraft-transport-7.99.14.jar
ChestTransporter-1.12.2-2.8.8.jar
ChickenChunks-1.12.2-2.4.1.71-universal.jar
CodeChickenLib-1.12.2-3.1.5.331-universal.jar
CraftingTweaks_1.12.1-8.1.6.jar
CraftTweaker2-1.12-4.1.2.jar
cxlibrary-1.12.1-1.6.1.jar
environmentalcreepers-1.12.1-1.2.1.jar
FinderCompass-1.12.1.jar
forestry_1.12.2-5.8.0.242.jar
GraveStone-1.12-Graves-1.0.13.jar
HammerCore-1.12.2-1.9.6.3.jar
Hwyla-1.8.23-B38_1.12.jar
InitialInventory-3.0.0.jar
ironchest-1.12.2-7.0.34.820.jar
jeibees-0.9.0.5-mc1.12.2.jar
jei_1.12.2-4.8.5.147.jar
journeymap-1.12.2-5.5.2.jar
JustEnoughResources-1.12.2-0.8.5.27.jar
legiblenei-1.4.12.6.jar
LLOverlayReloaded-1.1.4-mc1.12.jar
mcjtylib-1.12-2.6.3.jar
mods.txt
MouseTweaks-2.8-mc1.12.1.jar
MTLib-3.0.1.jar
Neat 1.4-15.jar
NoMobSpawningOnTrees-1.2.1-mc1.12.jar
NotEnoughItems-1.12.2-2.4.1.233-universal.jar
Pam's ClaySpawn 1.12a.jar
Pam's Get all the Seeds! 1.12a.jar
Pam's Llama Milking 1.12.2b.jar
Pam's Sheep Milking 1.12.2b.jar
RedstoneFlux-1.12-2.0.1.2-universal.jar
rftools-1.12-7.27.jar
signpost-1.12-1.06.1.jar
SolarFluxReborn_1.12.2-3.42r.jar
TimeHUD-1.12.2-7.3.0.jar
TorchLever-1.0.jar
UniDict-1.12.2-2.3.1.jar
WanionLib-1.12.2-1.4.jar
Wawla-1.12.2-2.5.251.jar
Weee! Flowers 1.12.2b.jar
WholeTreeAxe-1.12-1.7.1.jar

Sorry... I doesn't search in the first Storage Card.

Not a bug!